Automatic telephone system



Jan. 12, 1943. H. P. BOswAu AUTOMATIC TELEPHONE SYSTEM Filed Nov. 30, 1939 8 SheetS-Sheet l 2 INVENTOR. l e/L5 P Basal/aw ATTORNEYS.

Jan. 12, 1943.

AUTOMATIC TELEPHONE SYSTEM Filed Nov. 30, 1939 I 8 Sheets-Sheet 2 1N VENT OR.

192/25 PBoswaw ATTORNEYS. m

Jan. 12, 1943. 'H. P. BOSWAU 7 ,30 ,7 AUTOMATIC TELEPHONE SYSTEM Filed Nov. 30, 1939 a Sheets-Sheet s INVENTOR. Hans .P. .Zioswau WI/K'ZAM/ ATTogNEYs. 1

H. P. BoswAu AUTOMATIC TELEPHONE SYSTEM Jan. 12, 1943.

Filed Nov. 30, 1939 s Sheets-Sheet 4 I Wk k&

INVENTOR. .Zfans PBOSiZ/Qw BY NNQ .99

ATTORNEYS. m

Jan. 12, 1943. H. P. BOSWAU 2,307,751

AUTOMATIC TELEPHONE SYSTEM Filed Nov. 30, 1939 8 Sheets-SheetS INVENTOR. ffarzs 2? 3062062214 W i W ATTORNEYS.

Jan. 12, 1943. BQSWAU 2,307,757

AUTOMATI C TELEPHONE 5 Y8 TEM Filed Nov. 30, 1959 a Sheets-Sheet 6 A INVENTOR. 1622/23 f? Boswaw ATTORNEYS,

1943. H. P. BOSWAU AUTOMATI C TELEPHONE SYSTEM Filed Nov. 30, 1939 8 Sheets-Sheet 7 INVENTOR. [fa/2s P Beau/aw BY ATTORNEYS. 7

1943- H. P. BOSWAU AUTOMATIC TELEPHONE SYSTEM -8 Sheets-Sheet 8 Filed Nov. 30, 1939 INVENTOR. Hans P Boswaw shown. The opposite end Patented Jan. 12, 1943 AUTOMATIC TELEPHONE SYSTEM Hans P. Boswau, Lorain, Ohio Application November 30, 1939, Serial No. 398,929

55 Claims.

The present invention relates in general to automatic telephone systems, and the object of the invention is to produce anew and improved system of this character, which is economical to manufacture, easy to install, and which will give service of high grade with a minimum of maintenance expense.

A special object of the invention is the production of a new and improved switching mechanism for use in automatic telephone systems.

The invention and various features of improvement comprised therein will be described hereinafter in connection with the accompanying drawings, in which:

Fig. 1 is a partial side viewof a single unit of switching equipment; 7

Fig. 2 is a section on the line 22, Fig. 1, drawn to a somewhat larger scale;

Fig. 3 is a top view of the switching unit shown in Figs. 1 and 2, with certain parts broken away:

Figs. 4 to 7, inclusive, are views which show details of the supporting means for certain of the operating bars:

Fig. 8 shows' one of .the link operating members;

Fig. 9 is a fragmentary view of a switching.

unit in perspective, intended to facilitate an understanding of the principles on which it operates;

Fig. 10 is an exploded view of a part of the bank, showing the construction of the contact members and insulators; while Figs. 11 to 14, inclusive, show circuit drawings of a complete automatic telephone system using switching units of the type disclosed herein.

Referring now to Figs. 1 to 10, inclusive, the switching unit which is shown in these views will first be described.

The various parts of the unit are mounted on a frame which comprises vertical end members i and 2, of angle iron, and top and bottom members 3 and 4. The top member 3 is a fiat metal plate having upturned end 5, Fig. 1, which is secured to the vertical member I by screws, as is similarly upturned and is secured to the vertical member 2. The member 3 is also provided with upturned side flanges 8 and l. Th bottom member 4 is similar to member 3 and is provided with downturned ends l0 and I i which are secured to the vertical members i and 2, respectively. The bottom member 4 also has downturned flanges 8 and 9 along the sides. Thus a rigid frame is provided upon which all the ing unit are mounted.

The contact bank comprises ten parallel sections extending transversely of the switching unit and supported between the top and bottom plates 3 and 4. There is also a special section at one end of the unit, provided for a purpose parts of the switchwhich will be described subsequently. The complete bank consists in part of elements individual to each section and in part of common elements, the latter comprising rigid flat conducting bars extending lengthwise cf the switching unit through all the sections in series.

The contact bank may be explained more in detail in connection with Figs. 1 and 10. Considering the first regular bank section, there is a rectangular strip of insulation it which extends transversely across the bottom plate 4, and on this strip l4 there is placed a similar strip iii. Resting on the latter strip is a strip of conducting material l6, which has a series of eleven contact springs, such as l1, l8, l9, and 20, Fig. 10, formed integrally therewith. The complete strip IS with its integrally formed contact springs may be punched from a sheet oi suitable material. Each'of the insulating strips, such as I 4 and i5, may have an opening at each end, surrounded by a raised rim on the top of the strip, which is adapted to fit in an opening in a strip such as l6 and a corresponding depression inthe bottom of the next insulating strip above. This is a customary expedient used to assist in aligning the bank elements.

Above the conducting strip i 8 there is assembled an insulating strip 2|, which is similar to H except that its upper surface is provided with a plurality of notches for receiving the'contact element 22 and a series of ten conducting bars, such as 24, 25, and 26. The element 22 is provided with a terminal lug 23 which extends outside the bank assembly. There are nine other bank sections to the right of the first ection, which are identical with the first section. Fig. 1 shows the second section and part of the third, and also shows a special section at the left of the first regular section. In each of these sections the first fixed contact element at the edge of the bank is a contact element such as 22 which is individual to the section. In the special sectionand in .the secend section, Fig. 1, these contact eleinents are of the unit, and the projecting ends ofthe bars form terminals for the attachment of conductors.

The second layer of the bank is similar to the first, and in the case of the first regular section comprises the insulating strip 21, the conducting strip 28 having eleven integrally formed contact springs, such as 35, 36, 3'1, and 38, thenotched insulating strip 29, the fixed contact element 30 provided with lug 3|, and ten flat conducting 2 g bars, such as 32, 33, and-34 the latter being common to all the sections, like bars 24, 28, and 28 of the first level.

The third layer of the bank is also similar to the first layer, and comprises in the case of the first regular section the insulating strip 39, .the conducting strip 40 having eleven contact springs such as 48 .iormed integrally therewith, the notched insulating strip 4|, the fixed contact element 42 having lug 43, and ten fiat conducting bars, such as 44, 48, and 48. Thesebars are common to all the sections.

tional security, rods such as 58, Fig. 1, may be provided, passing up through the bottom plate 4 and through the openings, such as 43 and 58, in the bank-elements and threaded into the top plate 3. There may be one of these rods at each end of each bank section.

As previously mentioned, the line of trunk bars, such as 44, 32, and 24, extend to the right The conducting bars, 32, and 24- constitute a three-conductor line or trunk, bars 44 and 32 being the line bars while bar 24 i the test bar; that is, the two line conductors of a subscriber's line or of a trunk line may be connected to bars 44 and 32, while the test conductor is connected to bar 24. Thus it will be seen that the thirty bars in the first three layers of the bank represent ten three-conductor lines or trunks which are common to all sections of the bank. The three conducting strips 48, 28, and I8 of thefirst regular section are the three conductors oi! anintermediate trunk or link circuit which extends across or in coordinate relation to the ten lines or trunks represented by the ten sets of bars, such as 44, 32, 24, etc. Since the other nine regular sections of the bank are similar to the first section, there are in the first three layers of the bank ten of these intermediate link circuits each of which intersects each of the line or trunk circults. Any link circuit can be connected to any line or trunk circuit by operation of the contact springs at the point of intersection. For example, the link circuit in the first regular section can be connected to the first line or trunk circuit by pressing contact springs 55, 38, and 18 into engagement, respectively, with bar 44, 32, and 24. The manner in which this is done will be explained later on.

There are twenty-seven additional layers in the bank above the first three layers which have been described, making thirty layers altogether.

The additional layers may be considered as comprising nine sets of thre layers each. In each set of three layers there are thirty bars corresponding to bars such as 44, 32, and 24, representing ten three-conductor lines or trunks. Alsoin each set of three layers there are thirty conducting strips, such as 40, 28, and I6, three to each of the regular bank sections, and constituting ten three-conductor link circuits. In the complete switching unit there are, therefore, three hundred of the fiat conducting bars, such as 44, 32, and 24, representing one hundred three-conductor lines or trunks. There are also three hundred of the transverse conducting strips, such as 40, 28, and I6, arranged thirty to each regular bank section. Each such bank section, therefore, contains ten link circuits and, since there are ten regular bank sections, the total number of link circuits is one hundred.

The method by which the bank is built up may follow known practice in assembling such structures. It may be built up layer by layer on the bottom plate 4, as suggested in the previous de scription, and before the top plate 3 is assembled in the frame, suitable jigs being used for assisting in keeping the different sections in place as they are being assembled. When all the elements are in place the top plate 3 may be placed in position and pressure can be applied to compress the bank, after which the top plate 3 can be secured to the end members I and 2. Togive addibeyond the tenth regular bank section, and the ends of the bars are formed into terminal lugs for the attachment of wires or cable conductors. In Fig. 3 the ends of the top layer of bars can be seen, the end of top plate 3 being broken away, There are twenty-nine similar layers beneath the one shown.

As seen from the sectional view, Fig. 2, the three hundred line or trunk bars form ten vertical rows or groups of thirty bars each. The first group includes bars 24, 32,44, and twentyseven other bars in the same vertical row, the second group comprises bars 28, 33, 45, and twenty-seven other bars in the same vertical row, and so on. The numbering of the lines or trunks in each group may be from the top down. The first three bars in the first vertical row may be assigned to the first line or trunk, the next three to the second, and so on, bars 44, 32, and 24 being assigned to the tenth or 0 line or trunk of the group.

As previously mentioned, there are in each of the ten regular bank sections, ten intermediate link circuits, each comprising three conducting contact springs has associated with it a similar set of fixed contacts. The several sets of fixed contacts in the first regular section are all connected in multiple by strapping at the terminal lugs; that is, lugs 43, 3|, and 23 are connected, respectively, to the three corresponding lug of the contact set immediately above, and the latter three lugs are connected, respectively, to the next three lugs above, and so on. The ten contact sets of the first section thus strapped together constitute the multiple terminals of a trunk line, to which any link circuit or the first section may be connected by pressing its terminal contact springs, such as 48, 35, and I1, into engagement with their associated fixed contacts, such as 42, 38, and 22.

Each of the nine other regular bank sections is wired just as described in the case of the first regular section, and there are, therefore, ten trunk lines which terminate in multiply connected contact sets in the ten regular bank sections, respectively. These trunk lines may be outgoing trunks or incoming trunks, depending on the switching stage at which the unit is used, as will be explained in detail later on.

The special bank section which is shown to the left of the first regular section in Fig. 1 may be the same as the regular sections insofar as the contact elements contained therein are concerned. However, the function of this special bank does not involve the closing of any circuits to the line conductors, and hence the conducting strips which correspond to strips, such as 40 and V r 2,807,757 28, may be omitted, as indicated in the drawings.

Plain metal strips having no contact springs and functioning as spacers may be inserted instead. The first, fourth, seventhetc. layers are equipped with conducting strips such as 51, having contact springs, such as 58 and 54. At each of these conducting strip 51 terminating at lug 58 and having ten contact springs such as 54 constitutes means for extending a connection to the test conductor of any one of the ten lines or trunks of the bottom layer in the bank, and the other similar conducting strips above have the same functions with respect to the lines or trunks inthe corresponding layers of the bank.

The mechanism for operating the contact springs to the bank will now be explained, with reference particularly to Fig. 2, which shows a section taken just to the right of the first regular bank section as seen in Fig. 1. Considering the first vertical row of bars, such as 44, 82, and 24, with their associated contact springs, such as 55, 88, and I8, the latter are operated bylmeans Each .1 the ten regular as. section is,. of course, provided with a set of ten vertical operating bars similar to those described in the case of the first section. There are, one hundred of these operating bars.

The mechanism for raising the operating bars will next be described. To accomplish this purpose there is provided at each regular bank section a so-called gate and a magnet for operating therefore,

It. The gate and associated magnet at the first regular bank section is typical of the others and will be described briefly.

The magnet is indicated at I5 and includes core I8 and pole pieces 11 and I8 secured to opposite ends of the core. The magnet structure is mounted on the bottom plate 4 of the frame by means of brackets 82 and I8 secured to pole pieces I1 and I8 by screws 85 and 88, respectively, and to flanges 8 and 8 by screws 88 and 84, re-

spectively. The magnet has an armature I88,

pivoted on brackets 82 and I8 by means of pivot screws 81 and 88, respectively. Armature I88 has two arms IN and I82, which extend to the right of a vertical longitudinally movable operating bar having a plurality of projections thereon equal to the number of contact springs in the vertical row, or thirty altogether. This operating bar comprises a rod 88 on which there is molded a cylindrical body8| of insulating material having projections, such as 82, 83, and 84. There are ten of these operating bars assigned to the first bank section, as seen in Fig. 2.

The ten operating bars above referred to are provided with bearings which are supported on the top and bottom plates 8 and 4. The top plate is slotted at 81, Fig. 4, and the bottom plate at 88, Fig. 5, to permit the operating bars to be inserted after the bank has been assembled. The bars are, of course, inserted in-such a manner that the projections 82, 88, etc. are not interfered with by the bars 44, 82, etc., and are then rotated 90 to the positions in which they are shown. The upper bearing is formed by a notched strip 89 and a strip I8 having a single long recess in one side thereof, these strips being assembled from opposite sides of the row of bars 88 and being secured to the frame plate 8 by means of two screws. As can be seen from Fig. 6, the bars 88 lie in the notches II of strip 88 where they are retained by the strip I8. At its lower end each rod 88 has a rectangular bend formed therein, providing a short section such as 88 extending parallel to the main section of the rod, as shown in Fig. 5. The lower bearing is formed of a strip I2, having notches for each rod 88 and its parallel section 88, and a retaining strip 13. These strips are secured to the lower frame plate 4 by means of screws. It will be clear that the described arrangement prevents rotationof the rods 88.

The contact springs, such as I8, 38, and 55 are tensioned lightly against the projections, such as 82, 83, and 84. The projections 83, 84, etc.

rest on the bars 28, 32, etc., which support the a short distance beyond the pole pieces 11 and I8, as seen in Fig. 1. l

The gate comprises. two vertical pieces of angle material 8| and 82, which are pivoted on the upturned ends of arms lol and I82, respectively, by means of pivot screws 88 and 88, said pieces 8| and 82 being held together at the top by a cross member 84. The gate has bearings at the top comprising notches in the ends of strip 88, as shown in Figs. 2 and 6. When magnet I5 is energized, armature I88 is attracted and raises the gate, the vertical side pieces 8| and 82 sliding, in the notches in strip 88. When the magnet is released, the gate restofes by gravity and comes to rest with projections I 88 and I81 engaging fianges 8 and I of the top frame plate 3.

The magnet I5 has associated therewith a set of contact springs indicated at I88. The bracket 18 includes a part 88 extending at right angles to part I8 and having a downwardly-extending continuation 8| on which the springs I83 are mounted'by means of the usual insulators and screws. The springs are actuated by means of a stud I of insulating material carried on the arm I84 of armature I88.

Mounted onthe cross member 94 at the top of the gate there is a oomb-shaped'member 88 provided with the spring fingers such as 91. I These fingers are all lightly tensioned to the right against the cross bar 85 which extends across the gate a short distance below cross member 84. Each spring finger 8? is notched at one side, whereby there is formed at the end a lifting arm 88 the upper edge of which is located just to the right of and slightly below the hook 85 on rod 88. The relation between the liftingarms 88 and books 85 can be seen clearly from Figs. l and 2. These spring fingers and the lifting arms at the ends thereof are provided for raising the vertical operating bars 88.

As mentioned previously, there is a gate for .each regular bank section. or ten gates altogether.

One of the tens bars is indicated by the reference numeral H I. This bar and nine other similar bars extend lengthwise of the unit in spaced relation just above the upper frame plate 3. The bars are slidably supported at the left in notches in the transverse bar or strip I I2 and are retained therein by means of a strip H3. At the right hand end the bars are slidably supported in a notched bar which is similar to'bar H2 and are retained in position by a strip H4. All of the ten bars can be seen in Fig. 3, and also in Fig. 2, from which it will be clear that the bars are equal in number to and are spaced with definite relation to the spring fingers such as 91 on the gates. I

The bar III is forced to the right, as seen in Fig. 1. by means of spring H-5 and has an offset portion I I at the end which limits its movement in this direction by engagement with the edge of strip H3. The spring H is compressed between H the angle strip H6 at one end and the bar H6 at the other and being slightly longer than the distance between these parts it has a curved formation, as seen in Fig. 1. Each of the other nine bars such as bar III is provided with a spring such as spring H5, as can be seen clearly from Fig. 3.

The bar III is provided with an upwardly-extending projection or cam I2I which is located just to the right of the lower end of spring finger 91, as seen in Fig. 1, and with nine similar projections or cams, such as I22 and I20, which are located just to the right of the spring fingers corresponding to finger 91 on the nine other ates. respectively. These ten projections on bar III are adapted to bend the ten spring fingers such as 9! to the left and beneath the associated hooks such as 65 when the bar II I is moved longitudinally to the left. Each of the other nine tens bars is similarly provided with ten upwardlyextending projections which are adapted to operate the ten spring fingers in the corresponding IOW.

The tens bars described in the foregoing are selectively actuated by means of ten magnets, such as I3I. I32, and I30, which are mounted on the.

to frame plate 3 in a manner similar to the way in which magnets I5 are mounted on the lower frame plate 4.

Magnet I3I, which is the same as the others, includes the usual core I42 and pole pieces I31 and I38, which are secured to brackets I33 and I36 by means of screws I43 and I44, respectively.

The two brackets, in turn, are secured to the flanges 6 and I of top plate 3 by means of screws r I45 and I46, respectively. The magnet I3I has an armature 23 I, which is pivoted on brackets I33 and I36 by means of pivot screws I41 and M8, re-

spcctively The armature 23I has an upwardlyextending arm I40, for operating a set of contact springs which has been omitted in order to avoid obscuring the parts beneath it, and a downwardly-extending part I39 which merges into a transverse member 25I, Fig. 1, formed integrally therewith and spanning all the tens bars such as II I.

When the magnet I3I is energized the armature 23I is attracted and the member 25I is moved to the left, coming into engagement with a vertical member 24I riveted to the tens bar III and moving bar III to the left. Only bar III has a vertical member such as 24I associated with member 25I and consequently only the tens bar III is actuated by the energization of magnet I3I. The next tens bar has a vertical member 242 which is associated with the transverse member 252, actuated by the armature 232 of magnet I32, and each succeeding tens bar has a similar vertical member, which is, however. in

each case disposed one position 'to the right of the corresponding vertical member'on the preceding tens bar. Thus the armature of the tenth' or last magnet I30, seen in Fig. 3, has a transverse member which cooperates with the vertical member 240 on the tenth or last tens bar. From the foregoing it will be understood that the ten vertical members, such as 24I, 242, and 240, are positioned on a diagonal line, viewing the unit from the top, which extends from the first member 2 on the first tens bar to the last member 240 on the tenth tens bar. Each armature such as 23I is provided with a transverse member such as 25I spanning all the tens bars merely for the sake of uniformity, that is, to enable all the armatures to be made alike.

The bracket I33 includes a portion 233 which extends parallel to magnet I3I for a short distance and which has a vertical extension 234 on which a set of contact springs are mounted in conventional manner. These springs are shown in the case of magnet I32, and are indicated by reference character 236. They are operated by the insulating stud I4I' on arm I40 of armature 232. Each tens magnet is provided with a similar set of contact springs.

The operation of any tens bar results in the operation of mechanism shown in Figs. 1 and 3 for closing all the contacts in the corresponding vertical row in the special bank section hereinbefore described. The contacts in the row corresponding to tens bar III and including contact spring 54 are operated by means of a vertical operating bar comprising a rod H8 and a cylindrical body H9 molded thereon with projections extending underneath the contact springs such as 54. This operating bar may be similar to bar 6IJ-6I, Fig. 2, although only one-third of the side projections are used. The bar, HB-I I9 is supported in bearings the same as bar Bil-6i and the other bars in the same transverse row. The upper end of rod H8 is bent at right angles to the main portion of the rod and the short horizontal section thus formed carries a roller III which rests on the spring H5. When the tens bar III is actuated, that is, moved to the left, the spring H5 assumes a greater curvature and the roller H1 is raised, carrying with it the operating bar HIl-H 9. Thus all the contact springs such as 54 in the vertical row are operated.

There are nine other operating bars similar to bar Il8-I I9, all located in the same transverse row. The rollers such as ill for operating these bars can be seen in Fig. 3. I

It will be recalled now that each of the regular bank sections includes ten intermediate link circuits extending transversely of the unit. The lower link circuit of the first section comprises the conducting strips 40, 28, and I6, and terminates in the contact springs 48, 35, and I1, these three springs constituting a set. There are nine similar sets in a vertical row above the set of springs 48, 35, and H. The means for selectively operating these sets of contact springs will now be described.

There are ten operating members for the ten sets of contacts above referred to, each member comprising a recessed block of insulating material having projections thereon for operating the associated contact springs. Fig. 2 shows the first and second blocks I60 and I6I, and the last block I62. Block I60 will be described in detail. It may be molded in one piece of some plastic compound and has three projections I66, I61, and I68 which extend beneath the three contact springs I12, I13, and I14, respectively, of the associated set. These projections rest, respectively, on the three contact members, such as I16 and I11, which are immediately beneath them. On the side opposite the projections I66I68, the block I60 is recessed as indicated at I10, Figs. 2 and 8. There is also a longitudinal slot I69, having the same depth as recess I10. The slot I69 is of the proper width to receive the lateral extension 93 of the side angle member 9I of the gate. As shown in Fig. 2, this member is'wider where it passes the bank, the inwardly-extending portion being indicated at 93. The block I60 is thus loosely supported by the gate in the position shown in Fig. 2, with its weight resting on the contact members such as I16. The other blocks, such as I6I and I62, are supported the same way. It will be understood that when the gate is raised the part 93 thereof slides in the slots I69 of the several blocks and these blocks remain stationary. Means is provided, however, for moving a selected one of the blocks along with the gate when it is raised. The selecting means includes a set of ten socalled units bars whichwill now be described.

Seven of the ten units bars are shown in Fig. 1. The first two bars are indicated at I8I and I82, and the last or tenth bar at I80. For the purpose 'of supporting these bars there are provided two vertical strips I81 and I89 which in turn are supported on angle pieces I86 and I88, the latter being secured to the flanges 1 and 9 on the top and bottom plates of the frame. The angle piece I86 not only supports the strip I81, but also supports the units magnets, as will be explained presently. The strips I81 and I89 are slotted on the side toward the unit and the slots are deep enough to extend some distance beyond the edges of angle pieces I66 and I68, thus forming rectangular slots for receiving the bars, such as I8I, I82, and

' I80, as shown in Fig. 2. The bars fit loosely and are movable longitudinally to the left, as seen in Figs. 1 and 3. Each bar has a series of ten projections, such as I83, I84, and I85, which coperate with spring fingers on the gatesfor operating the blocks such as I60.

The particular block I60 is actuated by means of a spring finger I63, shown in Figs. 2 and 8. At its upper end the spring finger I63 is attached to the angle piece 9| of the gate for the first section. From its point of attachment to the gate the main body of the finger extends angularly downward until a point outside the block I60 is reached after which it extends vertically downward and terminates in an angularly disposed lifting arm I64, which extends to the right, as seen in Fig. 2. Just above the lifting arm I64 and in alignment with the projection I83 on bar I8I there is a projection or arm I65, which extends through opening I90, Fig. 1, in the gate. The parts I64 and I65 are formed integrally with the spring finger I63, which may be punched from a sheet of suitable material and bent to the shape shown.

When the units bar I8I is moved longitudinally to the left, the projections I83, I84, etc., engage the projections I65, I65, etc. on the upper spring fingers of all the gates and move them into operative relation to the associated blocks such as I60. The projection I83, for example, engages projection I66 and bends spring finger I63 far enough so that the lifting arm I64 enters the re.

cess I10 of the block. Now if the gate 9I.92 is raised, the angularly disposed lifting arm I64 will engage the surface I1I defining the upper side of the recess and will raise the block along with the gate, thereby pressing the contact springs I12, I13, and I14 into engagement with their asso ciated contact members such as I15. The other blocks, such as I6I and I62, remain unoperated.

The tens units bars such as I8I are selectively operated by means of a set of ten magnets which are mounted at the left hand end of the unit on the vertical angle piece I86. The magnet 2I I, associated with the first tens bar I8I, comprises the usual core and a heel piece 20I, the latter being secured to the angle piece by means of screws 209 and 2I0. The armature 202 has a knife edge pivot on the end of the heel piece 20I, and is provided with an extension 203 the end of which engages a notch in the end of bar I8I.

It will be seen that'when magnet 2 is energized, the armature 202 will be attracted and bar I8I will be moved longitudinally to the left by means of the armature extension 203.

Magnet 2 also operates a set of contact springs by means of the insulating pin 204 se-v cured to the armature 202. These contact springs are mounted on a bracket which forms part of heel piece 20I and comprises a part 205 bent at right angles to the main body of the heel piece and a part 206 which is bent at right angles to part 205 and which is parallel to the heel piece. The springs are secured to the part 206 by means of theusual insulators and screws. A spring 201 is inserted next to 206 and serves to retain the armature 202 in position.

As shown clearly in Fig. 1, each of the outer units bars suchas I82 has associated with it an operating magnet such as 2I2 which is similar to magnet H I. 1.

It should be stated that the sets'of contact springs which are shown associated with the gate magnets, tens magnets, and units magnets are tobe considered merely as indicating that each of these magnets may have and operate a set of contact springs in addition to performing its other function. The exact spring combination used in any case will depend on the switchin stage at which the unit is used and may vary even at each stage. The spring combinations used in a, representative system are described in connection with the circuit drawings.

The mechanical details of establishing a confiection by means of the described switching unit can perhaps be best understood by reference to Fig, 9, which shows in perspective a part of the units bar I8I are actuated, followed by lifting the gate 9|.

When tens bar II I is moved to the left, its projection I2I engages the end of spring finger 91 and bends the spring far enough so that lifting arm 98 passes beneath the hook 65 on vertical operating bar 606I. When units bar I8I is moved to the left, the projection I83 thereon engages arm I65 on spring finger I63 and bends the latter far enough so that lifting arm I64 passes underneath the edge I'II of the recess in block I60. Now when the gate 9| starts to rise, lifting arm 98 engages the hook 65 and slides along the hook a short distance until the arm engages the vertical portion of rod 60. The slight additional bending of spring finger 91 which is involved in this operation moves arm 98 away from projection I2I. At the same time the angularly disposed lifting arm I64 engages the inclined surface I1I on block I60 and slides along said surface until the lower end of spring finger I63 engages the angle piece 9I of the gate, thus moving arm I65 away from projection I83. Further movement of the gate now results in the raising of operating bar 606I by the lifting arm 98'and the raising of block I60 by the lifting arm I64.

The operating bar 60-6I, when raised as described in the foregoing, connects the ten lines terminating in the first vertical row of line bars to the ten intermediate link circuits in the first bank section, and more in particular it connects the line II to the uppermost or first link circuit by pressing contact springs I92, I93, and I94 into engagement with bars I95, I96, and I91, respectively. The first link circuit terminates in contact springs I12, I13, and I14, which are pressed into engagement with contact members I15, I16, and I11, respectively, by the block I60. Thus the line and trunk are connected.

The connection is' maintained by the gate 9I, which remains in operated position. The tens bar III and the units bar I6I are released as soon as the gate has operated. The spring finger 91 is retained in operative relation to bar 60-6I by the hook 65, and likewise the spring finger I63 is retained by the inclined surface "I on block I60. vWhen the gate is restored, the operating bar 666I and the block I60 are positively restored by the tension in the operated contact springs, such as I92 and I12. On complete restoration of the gate, the lifting arms 96 and I64 drop below hook 65 and surface I1I, respectively, and the spring fingers 91 and I63 are per-' mitted to restore.

As many as ten connections may be in existence simultaneously; that is, all ten of the trunks associated with the ten bank sections may be in use at the sametime. The establishment of all these connections is controlled by the tens and units bars, which are common to the ten gates. Further details of the way in which connections are established, dealing more particularly with the circuits involved, will b explained in connection with the description of the complete telephone system and its operation.

The circuit drawings, Figs. 11 to 14, inclusive, show a one thousand-line automatic telephone system using switching units of the type described herein, which function as finders, selectors, and connectors. The system may comprise ten groups of subscribers lines, each comprising one hundred lines, and each served by a switching unit operating in the finder capacity to connect calling lines to idle trunks. The finder stage therefore requires ten switching units. The trunks from the finder stage extend to a group of ten switching units operating as selectors, and from this stage other trunk lines extend to ten more switching units, one for each group of subscribers lines, which function as connectors. There may -be altogether thirty switching units,

The trunking between the different switching stages may conform generally to known pract ce.

The circuit drawings show diagramatically the apparatus and circuits involved in the establishment of a connection between a calling station A, Fig. 11, which is connected to a line in the second group of the'system, and a called station B, Fig. 13, which is connected to a line in the same group, together with sufficient additional appara tus and circuits so that the manner in which other connections are established may be readily understood. The telephone number at station A is 221 and that of station B is 212.

The line conductors 300 and 30I of the line of station A extend to the central office where they terminate in the individual line equipment comprising the line relay 306 and thecutofi relay 301. From the line equipment the conductors 300, 30I, and the test conductor 302 extend to the bars 3I6, 3I1, and 3I8 of the finder switching unit assigned to the second group of lines, and

three so-called normal conductors 303, 304, and 305 extend to the corresponding connector switching unit. The line and cutoff relays associated with lines having telephone numbers 222, 211, and 212 are also shown.

The first sub-group of subscribers lines, comprising lines munbered from 211 to 210, terminates in the first vertical group of line bars in the finder switching unit, counting from the left in Fig. 2, which may conveniently be referred to in order to explain how the lines are connected. Line No. 211 terminates in the first set of line bars at the top of this vertical row, while line No. 210 terminates in the bottom set of line bars, corresponding to bars 44, 32, and 24.

The second sub-group of subscribers lines,

comprising lines numbered from 221 to 210, terminates in the second vertical row in the same manner, the third sub-group of lines, numbered from 231 to 230, terminates in the third vertical row, and so on. The line bars 3I6, 3I1, and 3I8 to which the line of station A, Fig. 11, is connected are therefore the first three bars counting from the top in the second vertical row, as the finder switching unit is seen in Fig. 2.

Fig. 11 shows portions of the first and second regular bank sections and a portion of the special bank section. The vertical operating bar 32I, shown diagrammatically, corresponds to operating bar 60, Fig. 2, and bar 323 to the corresponding bar in the second bank section. Operating bars 322 and 324 are the second operating bars in the same transverse rows that include bars 32I and 323, respectively. That is, bars 32I and 323 are associated with the first sub-group of lines and bars 322 and 324 with the second sub-group of lines. Only three sets of line bars in each of two sub-groups are shown. Bars 3I9 and 320 are the first and second operating bars of the special section.

Fig. 11 also shows three blocks 325, 326, and 321 in the first bank section, which correspond to the first three blocks such as I60 in Fig. 2. The first three blocks in the second bank section are also shown. The three contact springs shown associated with each of these blocks constitute terminals of an intermediate link circuit, as previously explained. The three contact springs 344, 345, and 346, associated with block 325, are

row of the first section, to the first set of contact springs353, 354, and 355 in the second row, and so on. The multiple is shown as being composed of conductors 341, 346, and 349, but in reality the springs, such as 344, 350, 353, etc., are all formed from one continuous conducting strip, as previously described. The other link circuits are similar. In the special bank section contact springs 356, 351, etc., are formed of one continuous strip, whereby they are multipliedtogether.

.Conductor 358 in actual practive is connected to a lug such as 58', Fig. 1. This lug is part of a contact member to which the first contact spring 53' is soldered. Conductor 358 therefore connects to the conducting strip having contact springs 356, 351, etc., represented in Fig. 11 by conductor 361, by way of a lug such as 58', contact member 5|, and contact spring 53'. T? other conductors, such as 359 and 360, are con nected the same way.

The conductors 365, 366, and 361 constitute an outgoing trunk which extends from the first regular bank section to a selector unit. At the first regular bank section the trunk is connected in multiple to sets of contact members, such as 362, 363 and 364, which correspond to contact members I15, I16, and I11, Fig. 2. The conductors are actually terminated at lugs projecting from the sides of the contact members, as indicated in Figs. 1 and 10. There are ten outgoing trunk lines, of which the second trunk 368 is also-shown in Fig. 11.

Thedrawing, Fig. 11, also shows the first and second tens magnets 331 and 332, the first three units magnets 34!, 342, and 343, and thefirst two gate operating magnets 31! and 312. The relays 38l and 382 are two of ten guard relays associated with the ten outgoing trunks, respectively. Relay 331 is a control relay the function of which will be described.

The trunk line comprising conductors 365, 366, and 361 extends to a selector unit which is partly shown in Fig. 12, where it appears as an incoming trunk at the second regular bank section. This selectorunit is similar to the finder unit and consequently need not be described in detail. It will be desirable, however, to explain briefiy the trunking connections and certain other features.

There may be ten incoming trunks, terminating at the ten regular bank sections, respectively. Two of these trunks are shown, trunk 3389 which terminates in the first section and trunk 3tii361 which terminates in the second section, as previously stated.

The bars which extend lengthwise oithe unit and which in the finder unit correspond to subscribers'lines correspond to outgoing trunk lines in the selector unit, Thus the first vertical row of bars (ten sets of three bars each) are terminals of agroup of ten outgoing trunks which extend to the first connector unit. The first set of bars in this group comprises bars 450, 45!, and 452. The second vertical row of bars are terminals of a group of ten outgoing trunks which extend to the second connector unit. The first set of bars in this group comprises bars 453, 454, and 455. The other eight vertical rows (not shown) terminate outgoing trunks extending to the other eight connector units, respectively.

The drawing shows the operating bars 43!, 483, 482, and 484, which are associated with the first two vertical rows of the first two bank sections, and also shows operating bars 485 and 486 in the special bank section. The first two tens magnets are shown at m and m, and the first threeunits magnets at 44l, 442, and 443. Magnets 41! and 412 are the gate operating magnets for the first two bank sections.

The selector units handles calls partly on a numerical basis; that is, groups of outgoing trunks are selected in accordance with the initial digits in subscribers numbers, and therefore is provided with control units each of which includes digit registering means. One of these control units is shown at the left of Fig. 12 and comprises relays 400 to 4| I, inclusive, and relay 410. From the control unit ten marking conductors extend to the ten tens magnets, respectively, of the selector unit, these conductors being multiplied to the other control units for the same selector unit.. Two of the marking conductors are shown and are connected to tens magnets I and 432.

There may be two or three control units provided for each switching unit, or more if necessary, but in any case the number of such control units will be considerably smaller than the number of incoming trunks, and each control unit therefore will serve a plurality of trunks. All the incoming trunks, which are servedby the same control unit are normally connected in multiple to such unit, as shown in the case of trunks 360 and 365361, both of which normally extend to the control unit shown through contacts of their associated gate operating magnets 41! and 412. In order to give the subscribers themaximum access to the control units, each control unit is assigned trunks coming from different finder units. In other words, the outgoing trunks at each finder unit preferably all utilize different control units at the selector end and to attain this result may be routed in part to different selector units according to known trunking practice.

Relays 4H and M2 are sequence control relays. There is one of these relays for each contrunk extends to the connector unit, Fig: 13,

serving the second group of subscribers lines, where it is associated with the first regular bank section. The nine other trunk lines of the group extend to the same connector unit and terminate in the second to tenth bank sections. The connector unit is accessible from all the selector units and therefore the ten trunk lines ofthe group are multiplied in known manner to the other selector units. The same is true of the other groups of trunks outgoing from the selector units.

. 0nd group are connected to the line bars of the connector unit in the same way that they are Fig. 11.

connected to the line bars of the finder unit, Thus the line of station E, the telephone number of which is 212, is connected to the second set of line bars in the first group, these bars being indicated at 54s, and 54s.

The ten incoming trunks may be regarded as terminating in the ten regular bank sections, respectively, as previously stated, but since the trunks'do not extend directly to their respective bank sections, the arrangement may properly be explained briefly. Trunk 460-462, for example, normally extends by way of contacts of gate operating magnet 511 and trunk 510512 to the control unit which is shown in Fig. 14. When magnet 511 is energized, however, trunk 460462 extends to trunk 515511 (the latter terminating in the first bank section) by way of the battery feed unit comprising relays 520 to 523, inclusive. Each of the other incoming trunks is arranged the same way. Thus trunk 555, the only other trunk shown, normally extends to the control unit in Fig. 14, but upon the energization of gate operating magnet 512 it is extended to the second bank section by way ofthe battery feed unit 554.

There are a number of control units provided for the incoming trunks to the connector group, one of these units being shown in Fig. 14, as previously mentioned. The control unit shown comprises relays 600 to ,621, inclusive, also relay 510, and includes means for registering two digits in a called subscribers number. A group of ten marking conductors extends to the tens magnets of the connector switching unit and a similar group of ten marking conductors extends to the units magnets of the switching unit. Conductors 611 and 612 are two of the tens marking conductors, while conductors 661, 662, and 663 are three of the units marking conductors. Two additional conductors 613 and 614 extend to the switching unit as shown. All these conductors except conductor 614 are multiplied to other control units associated with the same connector unit.

Relays 621 and 622 are sequence relays, there being one of these relays provided for each of the control units.

The telephone system or exchange also includes the usual power equipment, such as ringing machine, busy signalling machine, and a source of current such as a storage battery with its charging equipment. This apparatus is well known and is not shown in the drawings. It is assumed that the positive pole of the storage battery is grounded. All circuit conductors shown as connected to ground are connected in practice to the positive pole of the storage battery, while all circuit conductors shown terminating in an arrow labeled negative are in practice connected to the negative or ungrounded terminal of the storage battery.

The operation of the equipment in establishing a connection between the line of station A, Fig. 11, and the line of station B, Fig. 13, will now be explained. When the receiver is removed'at station A, a circuit is completed over the line comprising conductors 300 and 301 for the line relay 306, the said circuit extending from ground ,by way of the left hand contact 308' of the cutoff relay 301, line conductor 301, talking instrumentalities at station A, line conductor 300,

right hand contact 312 of the cutoff relay, and

left hand winding of the line relay 306 to battery. Upon energizing, the line'relay connects the test conductor 302 to its own right hand ,ation of the operating bars 322, 324, etc.

the circuit continues through serially related.

chain contacts on all of the tens magnets to negative battery at contact 338 of relay 331. The continuity of the above circuit of course depends on no tens magnet being energized. Assuming that no tens magnet is energized when the line relay 306 pulls up, the closure of contact 308 completes the circuit for tens magnet 332 as described and the magnet energizes, looking itself at contact 333 and at the same time breaking the series chain circuit to prevent any other tens magnet from energizing.

The operation of the tens magnet 332 operates the second tens bar, thus preparing for the oper- The movement of the tens bar also raises the operating bar 320 in the special bank section, thus connecting the test conductors of all of the lines in the second sub-group to the units magnets. The test conductor 302' has been connected to battery by energization of line relay 306 as previously described, and accordingly a circuit is now closed for the units magnet 341 over a path which extends from ground by way of contact 339 of relay 331, serially related chain contacts on I all of the units magnets, left hand winding of magnet 341, rectifier 385, conductor 358, contact spring 351, bar 318, conductor 302, contact 310 of line relay 306, right hand winding of line relay and left hand winding of cutoff relay 301 to battery. The left hand winding of the units magnet 341 is of comparatively high resistance and accordingly the cutoff relay 301 is not energized over the above circuit. The units magnet 341 energizes, however, and closes a locking circuit through its right hand winding, at the same time breaking the chain circuit over which it was originally energized. vThis chain circuit, it will be understood, prevents more than one of the units magnets from energizing in the event that two subscribers lines in the sub-group should be calling at the same time. The energization of the units magnet 341 of course operates the associated units bar, which prepares for operation of the blocks 325, 328, etc. by their associated gates.

When the units magnet 341 is energized, a circuit is closed for the guard relays, such as 381, 382, etc., of all the outgoing trunk lines which are idle at the time. In the case of guard relay 381 the circuit extends from ground at contact 383, by way of serially related chain contacts on the ten guard relays, such as 381, 382, etc., lower winding of guard relay 381, rectifier 319, test conductor 361 of the first outgoing trunk line, normally closed contacts of the gate operating magnet 412, Fig. 12, contact 495 of relay 410, conductor 499, and normally closed contact 415 of the release relay 401 in the control unit to battery. If the second trunk line is idle, a similar parallel circuit extends through the lower winding of the guard relay 382 and over the test conductor of the second outgoing trunk to battery at the control unit in which this trunk line terminates. The same is true of the other guard relays; that is, the lower windings of all these guard relays are energized in parallel over their tery at the control units in which they. normally terminate. It will be assumed that the first outgoing trunk line is idle and accordingly the first guard relay MI is energized over the circuit traced. A plurality 01' other guard relays may start to energize at the same time,'but since relay SM is the first in the chain, it locks itself at its contact 818 and opens the chain circuit, thus preventing any of the other guard relays from fully energizing. On energizing, relay 38! prepares a circuitior relay 331 at contact 316 and at contact 816 closes a circuit for the first gate operating magnet 31L When the magnet 3H energizes, it'raises the gate associated with the firstbank section and thereby also raises the operating bar 322, thus connecting the ten lines of the second sub-group of subscribers lines to the ten intermediate link circuits of the first bank section. At the same time the gate raises the block 825, thereby connecting the first or uppermost link circuit to the outgoing trunk line associated with the first bank section, that is, to the first outgoing trunk line.

By these operations the conductors 800 and 30! of the calling line are extended by way of line bars 3H8 and 3H, contact springs 863 and 85%, contact springs 364 andttt, contacts 362 and 363, trunk conductors 385 and 856, and contacts 415 and 416 of the gate magnet 312, Fig. 12, to the winding of the line relay 60d of the control unit shown in Fig. 12. The line relay 600 is accordingly energized and at contact M3 closes a circuit for the slow-acting release relay dill. The latter relay, on energizing, disconnects the test conductor see from battery at contact tit and connects it to ground. The placing of ground on maintain magnet 8 in operated position.The guard relay 88i also breaks the circuit of relay 331. which accordingly falls back and again places battery on the'chain circuit associated with the tens magnets and ground on the chaincircuit associated with the units magnets. These magnets are accordingly placed in normal condition ready for responseto another callingline.

Before continuing with the operation, the purpose of the rectifiers which are included in the initial energizing circuits of the units magnets and the guard relays may be briefly explained. These rectifiers are provided in order to prevent false operation by so-called "sneak currents. In the case of the units magnets, for example, if the first line of the second sub-group is busy, there will be a ground on the test conductor 802, as explained in-the foregoing. Now, ii the second line in the sub-group makes a call, when the tens magnet is energized, the operating bar 320 is raised to connect up all the test conductors of the ten lines in the sub-group, thus establishing a circuit including the test conductor of the calling line, magnets 342 and MI in series, and the grounded test conductor of the first line. Since the units magnet MI is the first in the chain, it

the test conductor completes a holding circuitdd which extends back from the control unit by Way of conductor 99, contact ass of relay 610. contacts of gate magnet 612, test conductor 8811, contact 38d, contact spring 346 of the link circuit, contact spring 355 of the link circuit, bar BIS,

conductor 302, contact sit, right hand winding ground vfrom conductor 3m.

When the gate operating magnet 31! pulls up as previously described. it closes a circuit for relay 331 at contact 311. On energizing, relay 331 opens the circuit of the energized tens magnet 382, thereby permitting this magnet to deenergize. The operated tens bar is accordingly restoredto normal, and likewise the operating bar 320 in the special bank section. Relay 331 also opens the circuit of units magnet 36!, which deenergizes andrestores the operated units bar. On deenergiz ng, the units magnet 341 also breaks the circu t of the guard relay 38l which falls back and opens the initial energizing circuit for the gate operating magnet 31L This magnet remains energized, however, overthe previously described branch holding circuit, including resistance 318. The latter resistance is rather high and permits only sufficient current to fiow to would energize and lock and prevent the units magnet 342 associated with the calling line from energizing. This result is prevented by the rectifier 385 which prevents any how of current to the grounded test conductor 36? through magnets M2 and MI in series. In other words, the presence of these rectifiers in the circuits of the units magnets insures that each of these mag- I from battery on the test conductor of the sec-. ond outgoing trunk line by way of guard relays 382 and 38i in series to the grounded test conductor 361 of the first trunk line. No current can how in this circuit, however, because 01 the presence of rectifier 319. These rectifiers associated with the guard relays therefore insure that each guard relay can energize only over a circuit to ground through the chain contacts and the contact on an energized units magnet. In the foregoing explanation it has been necessary to take into consideration the actual direction of current flow, which is from the negative or ungrounded pole of the battery to the positive or grounded pole. This is a matter which is disregarded .in the conventional tracing of circuits. which by common usage are followed in the opposite direction.

Resuming the circuit description, the removal of battery from conductor 499 by the energizetion of the release relay 4M of the control unit, Fig. 12, has'the effect of making the trunk comprising conductors 365, 366 and 361 busy to other calls originated at the finder unit in Fig. 11. For instance, if another-call is made, and a circuit is closed for the guard relays 38l, 382, etc., the guard relay 381 cannot energize because there is no battery potential on test conductor 861. The removal of battery potentialfrom conductor 499 also makes busy all the,other trunk lines suchas 380, which normally terminate in .thesame control unit, and these trunks cannot be seized even though they are otherwise in idle condition. The reason for this will of course be clean When any trunk such as 365-361 is'taken for use, all the other trunks which use the same control unit must be made busy in order that the control unit may be reserved temporarily for the exclusive use of the call on trunk 365361.

The placing of ground potential on conductor 499 by'the energization of the release relay 491 01' the control unit not only establishes. a holding circuit in the manner described, but ground is also extended over the normal conductor 395 to the connector-unit, where the calling line is made busy.

. and 491' have energized, and the partially established connection is held by ground applied by the latter relay to conductor 499 and the holding its circuit is open at contact 312 of the eneigized cutofl relay. Y

The line 'circuit is maintained in the-described condition, with the cutoff relay 391 energized over the line, until the receiver is replaced at station A, or if the initiation of the call was caused by a short circuit on the line, until the short cir- 'cuit is removed. When the line is cleared the cutoff relay 391 falls back, and it another call is made the circuits will then mnctiorgin a normal manner. Although not shown in the drawings, arrangements may be provided for operating a signal whenever a line is locked out by energization of its cutofl relay under circumstances such as described. These arrangements may conveniently consist of a pilot relay connected in series with the right hand windings of each circuit in which said conductor is included. Ordinarily the calling subscriber will now start to dial the digits in the number 01' the called line. It may happen, however, that for some reason the dialing is delayed. The receiver may have been accidentally knocked off, or the initiation of the call may even have been due to a short circuit on the line. In such a case it is desirable to release the partially established connection in order to prevent tying up the control circuit and the incoming trunk lines associated therewith. The timer including cams 493 and 494 is provided in order to take care of this situation, and its is 212 and accordingly the first digit to be tact 4| 1 by way 01' the left-hand winding of relay'492 and operated spring 499 to battery. Relay 492 is energized over this circuit and establishes a locking circuit for its other winding at spring 419. In addition, relay 492 opens the ground connection to conductor 499 and substitutes therefor a new ground connection throughcontact 496 and spring.491. The holding circuit therefor now includes the ground connection at spring 491.

Alter the lapse of one half-minute, cam 493 again operates spring 491 and thus opens the holding circuit. The gate operating magnet 311 accordingly immediately deenergizes andbreaks the partially established connection. The opening of the line conductors is followed by the deenergization of relays 499, 491 and 492 in the control unit. The opening of the holding circuit also causes the immediate deenergization of line relay 396 but relay 391 is slow-acting and remains in operated position. When the relay 396 deenergizes, it connects ground to line conductor 391 at spring 398-, and at spring 3 it connects the right hand winding of the cutoff relay 391 to line conductor 399. Accordingly the cutofl relay 391 remains energized over'the calling line. The line relay cannot again energize due to the fact that group of cutoil relays. Such circuits are well known and since their inclusion would occupy space otherwise required, they "have not been shown herein.

It will be assumed now that the calling subscriber starts to dial promply after removing the receiver, it being recalled that the act of removing the receiver has resulted in the extension of the calling line through the finder unit and by way of an outgoing trunk to a selector unltwhere the trunk terminates in the line relay of the control unit shown in Fig. 12. The line and release relays 499 and 491 of the control unit are energized. The number of the called subscriber dialed is the digit 2 When the calling device is operated in accordance with the digit 2, two interruptions are produced in the calling line and the line relay 499 is deenergized twice. Rie

the locking circuit of relay 492 is broken, if this I relay should happen to have been energized, and.

a circuit is completed from ground by way of contact 413, contact 416, the winding of the slowacting relay 493, and contact 423' to battery. Relay 493 accordingly energizes and remains energized in known manner until the .dialing of the first digit is completed. 'Atits contacts 429 and 421 relay, 493, prepares a circuit for the first counting relay 495.

When the line relay energizes after the first interruption in the line circuit, it closes the previously prepared circuit for counting relay 495, said circuit extending from ground by way of contact 419 on the release relay 49l, contact 4 of the line relay, contact 429, chain contacts of counting relays499-496 in series, contact 42 I, and winding, of counting relay 495 to battery. Upon energizing, relay 495 locks itself at contact 424, so that its circuit is no longer dependent upon the continued energization of relay 493, and at contact 425 prepares a circuit for the second counting relay 496.

When the line relay 499 deenergizes in response to the second interruption in the linebattery. The completion or the last describedcircuit maintains the first counting relay 495 energized and also energizes the second counting deencu'gizations, respectively.

relay 400. Upon energizing, relay 400 prepares a holding circuit tor itseli at contact 420 nd prepares a circuit for the third counting re ay 401 at spring 421. i

When the line relay 400 energizes following the second interruption, it breaks the circuit which'includes the windings ofrelays 408 and 400 in series and therefore permits relay 400 to deenergize. At the same time, however, the line relay closes a holding circuit for relay 400, which extends from ground at M8 by way of H4, 420, chain contacts on relays 409, 400, and 401, contact 426, and winding of relay 400 to battery. The line relay 400 now comes to rest in energized position, with counting relay 400 energized.

Before continuing with the operation, it will be convenient to point out that the counting chain comprises five counting relays 405-409, inclusive, which are adapted to count the first five impulses in a series, and a transfer relay 410 by means of which the same five relays are enabled to count five additional impulses. means of five relays and a transfer relay therefor a, series of ten impulses may be counted. The

manner in which this is done may be briefiy explained, assuming that the digit is dialed instead of the digit "2.

When the digit 0 is dialed, ten interruptions are produced in the line circuit and the line relay therefore deenergizes ten times. On the third, fourth and fifth deenergizations, counting relays 401, 408 and 409 are energized in the manner described in the case of relay 400. When relay 409 is energized, it prepares a circuit at contact 100 for relay 4l0, which accordingly is energized on the sixth deenergization of the line relay. Relay 4l0 locks itself at contact spring 103. When relay 410 energizes, it also breaks its initial enashort interval this relay" falls back and "compl'etes a circuit -i'or relay 4'04 extending from ground at contact 418, winding of relay 404,

. contacts controlled :by spring 420 of relay 403,

chain contacts of relays 400, 408, and 401, contact 420 of relay 400, and winding of relay 400 ,to battery. ,The above circuit maintains'relay 406 energized. Relay 404 is energized in series 7 with relay 406 and at contact 423 breaks the circuit which has been prepared for counting relay 401, also breaking the circuit'o! relay 403 at contact 423'. The purpose of these operations is to prevent the energization oi relays 401 and 403 when the line relay 400 deenergizes upon the release of the control circuit. In addition, relay 404 closes a circuit for the relay 4 at contact 422.

ergizing circuit and the circuit of relay 409 at contact Ni, and relay 400 falls back, thus reestablishing. the chain circuit which extends back through contact 42! of relay 403 to relay 405. When the line relay energizes following its sixth deenergization, therefore, relay 405 is energized. It will be understood that relay M0 is so adjusted that contact 108 closes before contact .10" opens. On the seventh deenerglzation of the line relay, relay 400 responds, and relays 401, 400 and 409 respond to the eighth, ninth, and tenth Following the tenth deenergization, the line relay comes to rest in energized position with relay 409 energized.

The transfer relay 4I0 not only drops'relay 409 as described, but it operates to shift a control conductor from its normal association with the first five tens magnets into association with the second five tens magnets. For example, the second counting relay 400'is normally adapted to control the second tens magnet 432, but if the transfer relay M0 is energized, the second counting relay 405, now energized in response to the dialing of the digit 7" rather than the digit 2". is adapted to control the seventh tens magnet(not shown). The switching of the control circuit by the transfer relay M0 is accomplished at contact 102 in a manner which will be readily understood. Resuming the description of the establishment of the connection which is being set up, the first digit 2 of the called number has been dialed, resulting in the energization of the second counting relay 406 in the control unit shown in Fig. 12. Relays 400, 4M, and 403 of the control unitare also energized. When the dialing of the first digit is completed, the line relay no longer sends impulses to the slow-acting relay 403, and after Relay 4 'is a so-called sequence relay, one of which is provided for each .-of the control units. The purpose of these relays is to insure that the control units function one at a time in controlling the operation of the selector unit. The drawing shows the sequence relay 4H2 associated'with the'second control unit and indicates by the dotted portion of conductor 105 the presence of additional sequence relays. Ii no other sequence relay such as M2, for example, is energized at the time the circuit of sequence relay 4 is closed at contact 422, relay 4 will energize over a circuit which extends from ground at contact 422, winding of relay 4, contacts controlled by spring 431, conductor 100, chain circuit including contacts such as and 430 on all the sequence relays, and. resistance409 to battery. Upon energizing, the sequence relay 4 looks itself at contact 401 and breaks the chain circuit at contact 400, thus preventing any other sequence relay from operating. In addition to the foregoing, relay 4 completes a circuit extending from ground by way of contact 405,contact 102, contact 428, contact 429; and the winding of the tens magnet 432 to battery. Upon the closure of this circuit the tens magnet 432 is energized, thereby actuating the second tens bar and selecting the second group of outgoing trunk lines. that the operation of the tens bar is effective to raise the operating bar 400 inthe special bank section, thus connecting the test conductorsv or the trunk lines in the second group to the units magnets 441, 442, 443, etc.

The energization of sequence relay 4 also is effective to close a test circuit including the units magnet 44],- said circuit extending from ground at contact 422 by way of contact 434, conductor 449,. the' chain circuit including contacts of all the units magnets, conductor 489, winding of units magnet 44!, rectifier 441, conductor 488, contact spring 481 in the special bank section, bar 455, conductor 402, contacts of gateoperating magnet 0 at the connector unit, Fig. 13, contacts of relay 510, conductor 512, contact 021 of the release relay 60l of the'connector which are associated with idle trunk lines, that is, trunk lines which have their test conductors connected to battery at the control circuits in which they terminate.

It will be understood also the other units mag-Y It follows,- therefore, that all'ofthe units magnets which are associated with idle trunk lines start to energize responsive to the operation of the sequence relay-4i l. Assuming now. that the first trunk line is idle, relay 88! of the connector control unit, Fig. 14, being deenergized, the units magnet 44] will operate and will establish a looking circuit for itself at contact 448, at the same time breaking the chain circuit and preventing any of the other units magnets from energizing.

In addition, the units magnet 4 places ground at contact 448 on the test circuit including bar 455, thus making the selected idle trunk line busy. The resistance 828 at the connector control unit, Fig. 14, is high enough-to prevent excessive current flow. It will be understood also that the units magnet operates the first units bar, thereby preparing for operation all blocks such as 488 in the first horizontal row.

In addition to the operations described in the preceding paragraph, the units magnet 4 com- .pletes a circuit for relay 418, extending from ground at contact'444, conductor 448, contact 438 of relay 4, conductor'448 and winding of relay 418, to battery. Relay 418 accordingly energizes and at contact 485 removes the short ofthe gate-operating magnet is thus connected to the holding circuit and the magnet becomes fully energized, raising the gate and simultaneously lifting the block 488 and the operating bar 484.

When the gate-operating magnet 412 energizes,

the actuation of contact spring 414 and the make before break contacts associated therewith disconnects the incoming test conductor 381 from that part of the holding circuit which extends over conductor 488 toground at the control unit and at the same time extends said conductor 381 by way of contact 414, contact 483, spring 485,

and spring 488 to bar 455, which is now connected to ground by way of spring 481 and contact 445 or units magnet I. This establishes a temporary holding circuit which'maintains the connection until the line. and release relays in the connector control unit have had time to energize, as will be explained shortly. The right hand winding of gate-operating magnet 412 receives current from the holding circuit through contact 413, which maintains the magnet energized. It will be understood that contact spring 414 and associated contacts should be so adjusted that conductor 381 is not disconnected from conductor 488 until the gate is substantially fully operated, which will insure that springs 485 and 458 are actuated.

488 and 4 8I, contacts 5" and 582 01 gate-operating magnet 5", Fig. 13,- conductors M8 and and 8! I, and through the windings or the .line. relay 888 01' the connector control unit, Fig. 14, to battery and ground,- respectively. The line relay 888 is accordingly energized over the callin line and closes a circuit for the slow-acting re-, Q

lease relay 88l. Upon energizing, the latter relay disconnects the incoming test conductor 8|2 from its path to battery through resistance 828 and connects it instead to ground. The grounding of conductor 512 establishes a holding circuit extending back over conductors 812 and 482 to the selector unit, where conductor 482 is now connected to conductor 381, as previously explained. This holding circuit maintains the connection after the temporary circuit to ground at the units magnet I is broken by the release of the selector control unit, Fig. 12.

- The disconnection of incoming trunk conductors 385 and 388 from the line relay 488 oi the control unit by the operation 01 gate magnet 412 allows the line relay to deenergize and break the circuit oi! slow-acting release relay 48I which falls back also after a short interval and breaks the circuit of relays 484 and 488. On deenergizing, relay 488 breaks the circuit of tens magnet 432, which deenergizes and allows the associated tens bar to restore, thereby also restoring the operating bar 488 in the special bank section. Relay 484, on deenergizing, opens the circuit of units magnet 4, which deenergizes and allows The right hand winding The energi'zation of gate magnet 412 also shifts the contacts 415 and 418, whereby the line conductors 385 and 388 of the incoming trunk are disconnected from the line relay 488 of the control unit and are extended by way of contacts 481 and 488, springs 483 and 484, springs 458 and 451, bars 453 and 454, outgoing trunk conductors the operated units bar to restore at the same time as the operated tens. bar. The units magnet also opens the circuit of relay 418, which accordingly deenergizes. At the same time that relay 484 opens the circuit of the units magnet it opens the circuit of sequence relay. 4| I, This relay is made slow to deenergize in order to allow time for the tens and units magnets and their associated selecting bars to restore. After a short interval relay 4 deenergizes and closes the sequence relay chain circuit at contact 438. If a call is waiting on another control unit the associated sequence relay can now energize.

When the release relay 48I falls back, its circuit having been broken bythe line relay 488, it not only opens the circuit of relays 484 and 488, but also disconnects ground from conductor 499 and connects this conductor to battery at contact 5. Battery potential is thus applied by way of contacts of the now deenergized relay 418 to the test conductors of all the idle trunk lines which normally terminate in the control unit under consideration, thereby placing such trunk lines in selectable condition. Trunk line 388, for instance, may now be selected, but trunk line 38538| of course remains unaflected since the.

gate magnet 412 is in energized position and the trunk conductors are disconnected from thecontrol unit,

The calling line has now been extended to the line relay 888 oi the connector control unit, Fig. 14, and relays 8'88 and BM are energized. When the calling subscriber dials the second digit in the called number, or the digit "1," a single interruption is produced in the line circuit and the line relay momentarily deenergizes once, release relay 88! remaining in operated position due to its slowreleasing characteristic.

When the line relay falls back it closes a cir-- cuit for slow-acting relay 818 by way of contact 825, contact 828, contact 848, and winding of relay 8l8 to battery. Relay 8| 8 energizes and at contact 848 closes a circuit for slow-acting relay 

